Turbine vanes used in gas turbine engines orient the hot gases flowing through the turbine for efficient engagement with rotating blades downstream of the turbine vanes. A typical turbine vane includes an airfoil extending between an inner platform and an outer platform, wherein both platforms are integral to the turbine vane. The airfoil directs the flow into the array of rotating blades. The platforms provide the inner and outer flow surfaces that contain the flow of hot gases.
Exposure to the hot gases of combustion generates the need to cool the turbine vanes. Cooling fluid, typically bypass air drawn from a compressor upstream of the combustion process, is flowed through the hollow core of the airfoil to provide convective cooling. A plurality of cooling passages disposed in the airfoil provide means to flow the cooling fluid out of the airfoil and over the flow surfaces of the airfoil to provide film cooling of those surfaces. Platforms are typically cooled by impinging cooling fluid onto the surface opposite the flow surface. This cooling fluid may also flow through passages in the platform to provide film cooling of the flow surface of the platform.
An example of one type of platform cooling configuration is disclosed in U.S. Pat. No. 4,017,213, issued to Przirembel and entitled "Turbomachinery Vane or Blade with Cooled Platforms". This patent discloses a turbine vane or blade having a combination of impingement, convection and film cooling to cool the platform. In addition, this configuration includes an array of passages extending through the platform to convectively cool the trailing edge of the platform.
As combustion temperatures of modem gas turbine engines has risen, it has become increasingly necessary to provide as much cooling as possible to the platform, especially to the trailing edge of the platform. One problem encountered is that the trailing edge is typically downstream of a rail that attaches the turbine vane to the stator structure. Therefore, impingement cooling may not be possible in this region.
Another known configuration for cooling the platforms is shown in FIGS. 1 and 2. In this configuration, the trailing edge of the platform is cooled by flowing cooling fluid into a cavity that extends along the trailing edge of the platform. Cooling fluid exits the cavity through passages that direct the cooling fluid over the flow surfaces of the trailing edge. The cavity provides means to increase the cooling flow to the trailing edge and includes a plurality of trip strips to enhance heat transfer between the cooling fluid within the cavity and the platform. The general U-shape of the cavity is used to direct cooling fluid as close as possible to the corners of the trailing edge.
The above art notwithstanding, scientists and engineers under the direction of Applicants' Assignee are working to develop turbine vanes having configurations providing more effective cooling of the platforms.